Conventionally, color filters have been widely used in color liquid crystal displays. In these color filters, red, green and blue pixels are arranged generally in a mosaic pattern. For the fabrication of such color filters, known processes include the dyeing process, the printing process, the electrodeposition process, the below-described process using a photosensitive ink, in which a pigment has been dispersed, and so on. In particular, the above photosensitive ink-using process that forms pixels by photolithography, which uses the photosensitive inks each produced by dispersing a pigment together with a photosensitive resin and/or monomer, has become a mainstream process for the fabrication of color filters, because the resulting pixels are excellent in light fastness, heat resistance and solvent resistance owing to the use of the pigments as colorants.
In general, many of known pigments are usable in the above photosensitive ink-using process. For example, Patent Document 1 discloses as many as several tens of red, green, blue, yellow and violet pigments as colorants for color resist inks. Further, pigments to be used for the formation of individual pixels are generally selected such that the visible light transmission characteristics of the pixels will be in conformity with the luminance characteristics of light from a backlight. For example, desired transmission characteristics are imparted to the individual pixels by mixing a yellow pigment and orange pigment in predetermined proportions in addition to a red pigment in the case of the red pixels, mixing a yellow pigment in a predetermined proportion in addition to a green pigment in the case of the green pixels, and mixing a violet pigment in a predetermined proportion in addition to a blue pigment in the case of the blue pixels.
Under the circumstances of these days that there has been a desire of still higher brightness and saturation for color filters to meet an ever-increasing demand of higher definition, higher brightness and higher color reproducibility for liquid crystal displays in recent years, only an extremely limited fraction of these pigments, however, can show high-level brightness and saturation when employed in liquid crystal displays. For example, a violet pigment is often used together with Pigment Blue 15:6, a phthalocyanine blue pigment, in a color resist ink for blue pixels. As this violet pigment, Pigment Violet 23, a carbazole dioxazine pigment, is practically only one example that can be appropriately used, as disclosed in Patent Document 2.
This Pigment Violet 23 is frequently used to heighten the blue color purity of a copper phthalocyanine blue pigment that slightly transmits a green-color light, because its blue-color transmission range is located on the shorter wavelength side than that of a copper phthalocyanine blue pigment. In an approach that involves the mixing of two pigments of different transmission ranges, however, higher brightness and higher saturation are in a mutually-exclusive relation. The approach that employs Pigment Violet 23, the transmission range of which is significantly different from the copper phthalocyanine blue pigment and the transmittance of which is also low, involves a problem in that it cannot satisfy high-level brightness and high-level saturation at the same time. Moreover, Pigment Violet 23 is hardly dispersible as fine particles in a solvent and is high in polarizability, and therefore, is accompanied by a problem that, when mixed with a copper phthalocyanine blue pigment, the resulting blue pixels of a color filter are provided with a substantially-reduced contrast value, leading to a liquid crystal display equipped with deteriorated color display performance.
For color resist inks to be used upon fabrication of a color filter useful in a liquid crystal display or the like, it is essential to prepare colorants having transmission characteristics suited for its application purpose or object as described above. Accordingly, there has been a desire for a blue resist ink which makes use of a pigment other than Pigment Violet 23 and is useful for the formation of a color filter of higher contrast.    Patent Document 1: JP-A-5-281414    Patent Document 2: JP-B-2543052